1. Field of the Invention
The invention relates generally to the field of data processing system peripheral data storage devices, and more particularly to rigid disk storage subsystems.
2. Description of the Prior Art
Mass storage devices have existed for many years for large mainframe computer installations. More recently, the proliferation of mini and microcomputers has promoted a rapidly developing technology of smaller, relatively less costly, storage devices in an approximate range of five megabytes to 32 megabytes, to provide the increasing storage needs of users of these small computers. The need for these five to 32 megabyte storage devices has been further prompted as the availability of software and the sophistication of the users of these small computers have both increased.
Manufacturers of small computer systems generally assemble into a package a host computer and a group of peripherals devices, frequently including a hard disk drive for what is referred to as mass storage. The hard disk drive may be external to the cabinet containing the computer, or may be mounted within the same cabinet. Internal hard disk drives take up space which is at a premium within the main cabinet, but provide better reliability and less vulnerability as compared with external disk drives which are connected by long exposed cables.
The disk drives themselves have typically been made to interface with the electronics of the host computer through a standard interface referred to as an ST506 interface. Through implementation of the ST506 interface, sufficient definition has been achieved so that the disk drive can be treated as a "black box" defined by a specification and by the ST506 interface. The system manufacturer can purchase disk drives for integration into its system without concern for the details of the internal construction of the drive, and can purchase from various sources treating the disk drives as equivalent. Disk drives interfacing through the ST506 interface are referred to as "dumb" devices. That is, none of the control circuitry which establishes sector formatting, initiates head movement and selection, performs data buffering, etc. are provided in the disk drive. The "intelligent" control of the disk drive is provided by a disk drive controller which is on the host system side of the ST506 interface. The disk drive controller is typically manufactured by different suppliers than the disk drive manufacturers, and the disk drive controller typically treats the disk drive as a "black box" defined by a specification and the ST506 interface. The disk drive controller is often custom designed to interface with a particular architecture of the host computer system with which it is intended to work, but is able to work with most any disk drive that supports the ST506 interface. Disk drive controllers, therefore, tend to be host system dependent, and disk drive independent.
Supporting the ST506 interface places certain burdens on the total system. The rigidity of the standard stifles the opportunity to develop improvements in the disk drive which would require changes in the controller in order to utilize them. The conversion to and from the ST506 bus also utilizes power and requires additional components, increasing both heat generation and risk of failure. In addition, separating the intimate relationship between the drive and the controller with a standard interface causes possible problems of small production variations causing incompatibility between a particular drive/controller pair.
One example of a requirement placed on a disk drive by the ST506 interface is the track 0 sensing switch. When a disk drive is first powered up, the head could be anywhere on the disk. It is necessary to first locate the head, after which various methods may be used to keep track of its location. The ST506 interface has built into it a requirement of a track 0 sensing switch to locate the head when it is at the track 0 position. Track 0 sensing switches are subject to delicate adjustment, and alternate methods of locating the head could improve reliability. The ST506 interface is a limiting factor in that regard, however. Although controllers can be made which do not utilize the track zero sensing switch, a disk drive must have the track zero switch to fully support the ST506 interface.
If the standard interface approach were moved to the host system/controller side of the controller, instead of on the controller/disk drive side of the controller, and if the controller were integrated into the disk drive, substantial advantages over the prior art would be realized.